Matrix dimensions in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function in R is used to find the dimensions of a matrix?

The dim() function returns the number of rows and columns of a matrix as a vector.

beginner

How do you create a 3x2 matrix in R?

Use matrix(data, nrow = 3, ncol = 2). For example, matrix(1:6, nrow = 3, ncol = 2) creates a matrix with 3 rows and 2 columns filled with numbers 1 to 6.

intermediate

What does dim() return if applied to a vector in R?

It returns NULL because vectors do not have dimensions like matrices do.

intermediate

How can you change the dimensions of a vector to make it a matrix?

Assign a dimension attribute using dim(vector) <- c(rows, columns). For example, dim(v) <- c(2,3) turns vector v into a 2x3 matrix.

beginner

What is the difference between nrow() and ncol() functions in R?

nrow() returns the number of rows of a matrix, while ncol() returns the number of columns.

What does dim(matrix(1:6, nrow=2, ncol=3)) return?

A [1] 2 3

B [1] 3 2

C [1] 6

D NULL

dim() returns the number of rows and columns. Here, 2 rows and 3 columns.

If v <- 1:6, what does dim(v) return?

A 6

B NULL

C [1] 1 6

D [1] 6 1

Vectors do not have dimensions, so dim() returns NULL.

How do you convert a vector v of length 6 into a 2x3 matrix?

A Use <code>dim(v) <- c(2,3)</code>

B Use <code>matrix(v, nrow=3, ncol=2)</code>

C Use <code>length(v) <- c(2,3)</code>

D Use <code>dim(v) <- c(3,2)</code>

Assigning dim(v) <- c(2,3) changes the vector into a 2-row, 3-column matrix.

What does ncol(matrix(1:4, nrow=2)) return?

A 3

B 4

C NULL

D 2

ncol() returns the number of columns. Here, the matrix has 2 columns.

Which function gives the number of rows in a matrix?

A length()

B ncol()

C nrow()

D dim()

nrow() returns the number of rows in a matrix.

Explain how to find and change the dimensions of a matrix in R.

Think about how you check size and how you can turn a vector into a matrix.

Describe the difference between a vector and a matrix in terms of dimensions in R.

Consider what dim() returns for each.